ci: fix backfill-corr-ci to R 4.3

Author: dshemetov

.github/workflows/backfill-corr-ci.yml

@@ -17,7 +17,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     if: github.event.pull_request.draft == false
     defaults:
       run:
@@ -26,10 +26,11 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Set up R
+      - name: Set up R 4.3
         uses: r-lib/actions/setup-r@v2
         with:
           use-public-rspm: true
+          r-version: 4.3
 
       - name: Get date
         id: get-date